Retinal and other types of eye injury can occur from inadvertent direct exposure to the optical signals used in present communication systems. Danger is presented by the power and the wavelength of such signals. Generally, these systems operate with signals having relatively high power concentrated in a tiny beam located outside the visible region.
Recent developments in optical networking have only heightened existing safety concerns. For example, optical amplifiers and other optical components are now being developed to drive optical signals to even higher output power levels. Multi-wavelength systems are also a concern because the total optical power in the optical fiber is the sum of the powers of the individual wavelength components. Consequently, optical systems having total output power of 20 dBm or more are now being realized as a result of advances in optical amplifier and multi-wavelength optical networking technologies.
Because the extent of injury is most likely proportional to the total output power and the time of exposure, it is necessary to quickly shut off or reduce the output power of a network element in the event of a fiber cut, removed connector, or any other discontinuity in the optical path. In prior arrangements, control of upstream elements relies entirely upon downstream elements nearer to the fault. For example, downstream network elements perform fault detection and localization by monitoring the degradation or interruption of the forward propagating signal, i.e., the signal propagating downstream. If such a degradation or interruption is detected, the network control and management system then communicates the necessary supervisory signals to switch off the upstream network element. This scheme is limited in several ways. First, the scheme will only work for faults that occur between the upstream and downstream elements. Secondly, this scheme will fail if, by virtue of the system failure, the downstream element cannot communicate with the upstream element, e.g., if the supervisory channel is lost as a result of the discontinuity in the optical path. Even if this scheme works, there are other issues of added cost and complexity for such control and the possibility of delay in effecting control.